156 Mb. E. Hunt on certain Phenomena connected with 



centre of the ring would move round the centre of attraction once for 

 every revolution of the ring. In other words, the ring would revolve 

 about the centre of attraction instead of about its own centre, and the 

 centrifugal force would be least on the side nearest the centre of attraction, 

 and greatest on the opposite side ; and this would aid the attractive 

 force in bringing the side of the ring nearer to the centre of attrac- 

 tion. Mr. Elliot says that the point of the ring nearest to the centre 

 of attraction at one instant, will, after a portion of a revolution, be 

 nearer to the centre than it would have been if not attracted to it ; and 

 he assumes that, in its second position, it is a new nearest point, with- 

 out proving that a point following it is not nearer than it. It appears 

 from Mr. Elliot's paper that he described or exhibited apparatus show- 

 ing the motion of Saturn's ring on a small scale, the ring being repre- 

 sented by an iron ring, and the centre of attraction by a magnet. If, 

 however, the construction of this apparatus is studied it will be found 

 not by any means to exhibit the conditions of Saturn's ring. The 

 apparatus is in fact a mere modification of the gyroscope or peg top, 

 and it requires to be proved that Saturn's ring is really under similar 

 conditions ; but even if this were proved, the explanation which fails in 

 the case of the peg top must also fail in that of the ring. In Mr. 

 Elliot's apparatus the ring is placed upon a spinner which is supported 

 upon a small pedestal. The lower part of the spinner reaches below 

 the point of support, and is weighted to bring the centre of gravity 

 of the spinner and ring into coincidence with the point of support, 

 which is a short distance below the ring. The description does not say 

 whether or not the ring is fixed to the spinner, but it does not much 

 matter. The magnet is made to project downwards inside the ring, and 

 when placed eccentrically of course attracts one side of the ring more 

 than the other. If the ring is fixed to the spinner, the attraction of the 

 magnet obviously tends to make the spinner turn about its point of 

 support in a vertical plane, and this tendency combines with the original 

 rotation to produce a modification of the precessional movement shown 

 by the gyroscope. If the ring lies loosely on the top of the spinner, it 

 wiU either tend to tilt over the spinner by its frictional adliesion, or if 

 it slips on the top of the spinner, it will cause a preponderance of weight 

 on one side, and in any case produce the same precessional movement. 

 As in the gyroscope the ring would not be prevented from appi-oaching the 

 magnet were it not for the reaction on the point of support of the spin- 

 ner, and unless something equivalent to that reaction, on the point of 

 support in the model, can be shown to exist in the case of Saturn's ring, 

 the latter cannot be considered as represented by the former. In the 

 model the magnet tends to change the plane of motion of the ring, but 



